For the second ability, you choose the target artifact or creature as you activate the ability. You choose whether to sacrifice an artifact and which artifact to sacrifice as the ability resolves.

8/23/2016

For the last ability, if you choose an artifact on the battlefield as the target, and that artifact is no longer on the battlefield as the ability tries to resolve, the ability will be countered and none of its effects will happen. You won’t get any tokens. This is true even if the card that represented that artifact is now in a graveyard. That card will be a different object than it was on the battlefield.